1. Field of the Invention
The present invention relates to a low pressure EGR system control apparatus that calculates a relative humidity from an atmosphere temperature and determines whether humidity is high or not according to a driver's driving behavior to limit an operation of a low pressure EGR system and the method thereof.
2. Description of Related Art
An internal combustion engine is provided with an exhaust gas recirculation (EGR) system that recirculates a part of an exhaust gas into an intake system such that a temperature of burning gas in the combustion chamber can be lowered so as to reduce the generation of NOx.
FIG. 1 is a drawing showing an EGR system that is disposed in an internal combustion engine.
As shown in FIG. 1, a high pressure EGR system recirculates an upstream side exhaust gas of a turbocharger 102 that is connected to an exhaust manifold of an engine 100 to an intake system and a low pressure EGR system 120 recirculates an downstream side exhaust gas of a catalyst 103 to an upstream side of a compressor.
The high pressure EGR system 110 is duty controlled according to a driving condition of the engine 100 to include a first EGR valve 111 that controls a flow rate of an upstream side exhaust gas of a turbo charger 102 and a first EGR cooler 112 that cools a recirculated exhaust gas passing the first EGR valve 111, and the cooled recirculated exhaust gas is supplied to an intake manifold.
Also, the low pressure EGR system 120 is duty controlled according to a driving condition of the engine 100, includes a second EGR valve 121 that controls a recirculated flow rate of an downstream side exhaust gas of a catalyst 103, a second EGR cooler 122 that cools exhaust gas flowing through the first EGR valve 121, and a filter 123.
The low pressure EGR system 120 recirculates a downstream side exhaust gas of a turbocharger 102 and supplies a larger amount of exhaust gas without deteriorating a turbe efficiency in a high load/speed driving condition to reduce NOx and fuel consumption.
However, the low pressure EGR system forms condensate in a heat exchanging process that the recirculated exhaust gas passes the EGR cooler and the intercooler and the condensate amount is determined as follows.
The condensate generation amount=vapor amount included in exhaust gas(g)−saturated steam amount in a dropped temperature (g/m3)×exhaust gas flow rate (m3)
FIG. 2 is a drawing showing a condensate generation factor and a problem thereof in a low pressure EGR system.
As shown in FIG. 2, factors that indirect affects a condensate generation in a low pressure EGR system includes a coolant temperature, a low pressure EGR cooler efficiency, a pressure difference, a load, a fuel consumption amount, an atmosphere temperature, a vehicle speed, an atmospheric pressure, a boost pressure, in intercooler efficiency, a relative humidity, an EGR ratio of a low pressure side and a high pressure, etc.
And, factors that direct affects a condensate generation includes a downstream side temperature of a low pressure EGR cooler, an exhaust gas flow rate of a low pressure EGR cooler, a vapor amount of an operating fluid, a downstream side temperature of an intercooler, an intercooler passing flow rate, etc that are affected by the indirect factors.
Accordingly, a condensate is generated in a low pressure EGR cooler by the indirect factors and the direct factors.
The condensate that is formed in the low pressure EGR cooler damages a compressor wheel of a turbocharger, corrodes a low pressure EGR valve and a low pressure EGR cooler, and closes a filter.
And, the condensate that is formed in the intercooler corrodes the intercooler and can damages components around a combustion chamber.
The condensate that is formed in an intercooler is stored in a reservoir tank, if the condensate reaches a predetermined level, an electric valve is automatically operated to exhaust the condensate in an U.S. Pat. No. 6,301,887.
Also, an exhaust passage is formed in a low pressure EGR cooler to exhaust condensate in a Japanese Patent Laid-Open Publication No. (JP2008-002351) such that the generated condensate is exhausted through an exhaust pipe.
There is a problem that the added system increases an entire system price in this conventional art.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.